Display screen or portion thereof having a graphical user interface



The sole FIGURE is a front view of a display screen or portion thereof having a graphical user interface showing my new design.

The outermost broken-line rectangle depicts the perimeter of a display screen or portion thereof having a graphical user interface and forms no part of the claimed design. The remaining broken lines depict portions of a graphical user interface and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof having a graphical user interface, as shown and described. 